Why Is Homo floresiensis Still Such a Mystery?

Cosmos Magazine has an article by Debbie Argue, biological anthropologist from Australian National University, about Homo floresiensis and why it has been a struggle to accurately and adequately place this hominin within the framework of human evolution.

 Here was the initial assessment:

Peter Brown and colleagues originally proposed two competing hypotheses about the origins of H. floresiensis. One is that the species is an early hominin similar to the earliest identified in the Homo genus. The fossils for these species are known only from Africa and are between one and two million years old. This implies that the ancestors of H. floresiensis could have got to Flores Island in the vicinity of a million years ago and survived there until at least 60,000 years ago.

Their alternative hypothesis was that H. floresiensis is a dwarfed descendant of Homo erectus, which is the only known non-sapiens hominin to once have existed in Indonesia. Its remains have been found on the island of Java. According to this view, the dwarfing of H. erectus was an evolutionary response to being isolated on an island with a limited food supply. Just as the Asian elephant evolved into the dwarfed Flores stegodon after becoming marooned on the island, H. erectus could have met a similar fate.

It was also proposed that this hominin might have expressed microcephaly.  This idea failed to explain other aspects of the skeleton, however, such as its diminutive height (around 3 feet), long arms and feet and primitive skull features. Here is an image of H. floresiensis compared to a modern human, who had been running around the landscape for at least 100k years while H. floresiensis was extant.

This all saw at least some resolution with the discovery and description of some remains  on another areas of the island Flores that were very similar to the H. floresiensis remains but dated to some 600 thousand years earlier than the remains in Liang Bu.  This lent more credence to the idea that H. floresiensis was, in fact, an offshoot of Homo erectus.

So, Argue, along with Colin Groves, Bill Jungers and Mike Lee, performed statistical tests (this story does not say which kind, a peculiar omission) on a number of different hominin species, comparing them to H. floresiensis.  What did they find?

We therefore hypothesise that H. floresiensis shared a common ancestor with H. habilis. We do not know who that ancestor was or when it lived, but it would have to be older than the oldest H. habilis specimen known, so older than 1.75 million years. The implication is that the H. floresiensis ancestor evolved before that time in Africa, dispersed from that continent, and arrived on Flores earlier than 700,000 years ago, judging by the age of the jaw and teeth found at Soa Basin. This represents a hitherto unknown movement of very early hominins out of Africa.

Presently, the earliest evidence for hominins outside of Africa come from Europe, the Near East and Asia, and date to between 1.5 and 1.8 million years ago. Argue's hypothesis would suggest that H. floresiensis appearance in east Asia represents a separate migration out of African sometime either before or after the wave that saw Homo erectus show up in Trinil and Sangiran, in Indonesia.

Questions still abound as to why this species never saw the evolutionary trajectory that other hominins went through in terms of cranial expansion, increase in height and changes in brachial and crural indices. On the other hand, if evolution proceeds through what we have termed systematics, then advanced traits will show up in related species and if the ancestors of H. floresiensis were cut off, they would just go on their merry way.  We know that such a pattern holds for H. naledi, in South Africa, which coexisted with archaic Homo sapiens, in some way, shape or form. 

The article ends on a very peculiar note, in which she suggests the remote possibility that H. floresiensis is still alive out there, somewhere:

Could the Hobbit still exist in the wild mountain forests of Flores? When H. floresiensis was announced, the media picked up on the local folklore that small human-like creatures roam the forests. Descriptions of sightings are well recorded and quite detailed. The similarity to H. floresiensis is intriguing. But most researchers would say ‘show me the bones!’

This reminds one of the stories involving the Yeti/Sasquatch/Abominable Snowman, which likely derive from the finding of the bones of the Miocene ape Gigantopithecus, which was close to ten feet tall, when standing.  Is H. floresiensis still out there?  Probably not, but I am sure that the cryptozoologists haven't given up hope. 

Homo floresiensis Gains Legitimacy

Science Daily has posted a story detailing new examination of the Liang Bua crania by researchers at SUNY Stonybrook, The University of Tubingen, and the University of Minnesota in which they grant legitimate species status to Homo floresiensis.  They write:

The scientists applied the powerful methods of 3-D geometric morphometrics to compare the shape of the LB1 cranium (the skull minus the lower jaw) to many fossil humans, as well as a large sample of modern human crania suffering from microcephaly and other pathological conditions. Geometric morphometrics methods use 3D coordinates of cranial surface anatomical landmarks, computer imaging, and statistics to achieve a detailed analysis of shape.

This was the most comprehensive study to date to simultaneously evaluate the two competing hypotheses about the status of Homo floresiensis.

The study found that the LB1 cranium shows greater affinities to the fossil human sample than it does to pathological modern humans. Although some superficial similarities were found between fossil, LB1, and pathological modern human crania, additional features linked LB1exclusively with fossil Homo. The team could therefore refute the hypothesis of pathology.

The link to the PLoS paper is here.This is the conclusion of the paper:

Our analyses corroborate the previously suggested link between LB1 and fossil Homo and support the attribution of this specimen to a distinct taxon, H. floresiensis. Furthermore, the neurocranial shape of H. floresiensis closely resembles that of H. erectus s.l. and particularly specimens of early Eurasian H. erectus, although it is unclear whether this latter affinity is best attributed to a close phylogenetic relationship or to a size-related convergence in shape. These results also counter the hypotheses of pathological conditions as the underlying cause of the LB1 neurocranial phenotype, with the possible exception of posterior deformational plagiocephaly, a condition without significant adverse health effects.

Of course, this doesn't mean that it is not endemic dwarfism, just that it is not built on a modern human base. In this case, it may represent a Homo erectus base. Why it was so marked is still an unanswered question.It is also quite possible that this represents founder effect followed by years of selection for diminutive characteristics.  It definitely represents a peculiar side branch in human evolutionary history but not one that defies explanation.